-Last night, filled tank in 2000 Sephia with no previous signs of
malfuntion.  Drove home and parked it for about an hour.

-Upon ignition, engine sputtered, but idled OK.  During acceleration, ran
very rough.  After about three blocks, turned around and drove the trusty
Volvo for 20 mile trip instead.

-This morning, drove Kia about 2 miles to buy new fuel filter.  On the way,
noted that sputter occured in mid-throttle.  Replaced filter, and restarted.

-Let idle for several minutes and increased throttle.  Sputtering still
occuring.

-Car has 52K miles.  Bosch plugs and K&N filter only a few months old.

What next?